1 

MEMORANDUM 

DATE: June 22, 2015 

SUBJECT: Section 112(d)(6) Technology Review for the Final Wool Fiberglass NESHAP 

 

FROM: Susan Fairchild, EPA/OAQPS/SPPD/MMG 

TO: Docket EPA-HQ-OAR-2010-1042 

1.0 Introduction 

This memorandum presents the results of a review on the developments in practices, processes, 

and control technologies that apply to wool fiberglass manufacturing, and specifically to sources 

subject to the national emission standards for hazardous air pollutants (NESHAP) for Wool 

Fiberglass Production (40 CFR 63, subpart NNN). This analysis is part of the U.S. 

Environmental Protection Agency’s (EPA’s) review efforts in accordance with section 112(d)(6) 

of the Clean Air Act (CAA). Section 2 of this memorandum provides background information on 

the requirements of section 112(d)(6) of the CAA, the wool fiberglass source category, and the 

requirements of the Wool Fiberglass NESHAP. Section 3 discusses the review of information on 

developments in practices, processes, and control technologies that have occurred since the 

original development of this NESHAP. Section 4 summarizes the technology review findings. 

2.0 Background 

2.1 Requirements of Section 112(d)(6) of the CAA 

Section 112 of the CAA requires the EPA to establish technology-based standards for sources of 

hazardous air pollutants (HAP). These technology-based standards are often referred to as 

maximum achievable control technology, or MACT, standards. Section 112 also contains 

provisions requiring the EPA to revisit these standards. Specifically, CAA section 112(d)(6) 

states: 

(6) REVIEW AND REVISION. – The Administrator shall review, and revise as 

necessary (taking into account developments in practices, processes, and control 

technologies), emission standards promulgated under this section no less often 

than every 8 years. 

For the purpose of this technology review, a “development” was considered to be any of 

the following: 

• Any add-on control technology or other equipment that was not identified and considered 

during the development of the NESHAP; 

• Improvements in add-on control technology or other equipment that were not identified 

and considered during NESHAP development that could result in significant additional 

HAP emissions reductions; 
2 

• Work practice or operational procedure that was not identified and considered during 

NESHAP development; and 

• Process change or pollution prevention alternative that could be broadly applied that was 

not identified and considered during the development of the NESHAP. 

2.2 Description of Source Category and NESHAP Requirements1

Wool fiberglass manufacturing is the high-temperature conversion of various raw materials into 

a homogeneous melt, followed by the fabrication of this melt into glass fibers. Wool fiberglass 

production can be segmented into three phases: raw materials handling, glass-melting, and wool 

glass fiber forming and finishing. The primary component of glass fiber is sand, but it also 

includes varying quantities of feldspar, sodium sulfate, anhydrous borax, boric acid, and many 

other materials. In the glass-melting furnace, the raw materials are heated to a high temperature 

and are transformed through a sequence of chemical reactions to molten glass. Although there 

are many furnace designs, furnaces are generally large, shallow, and well-insulated vessels that 

are heated from above. In operation, raw materials are introduced continuously on top of a bed of 

molten glass, where they slowly mix and dissolve. Mixing is effected by natural convection, 

gases rising from chemical reactions, and, in some operations, by air or oxygen injection into the 

bottom of the bed. Oxygen is also used as a fuel and replaces air at some furnaces. 

Glass-melting furnaces vary in fuel source and method of heat application into four types: 

recuperative, regenerative, unit, and electric melter. Prior to 1999, the recuperative, regenerative, 

and unit melter furnaces could be fueled by either gas or oil and could supplement those fuels 

with oxygen. Current industry technology no longer shows the use of oil as a fuel for glassmelting furnaces. Recuperative furnaces use a steel heat exchanger, recovering heat from the 

exhaust gases by exchange with the combustion air. Regenerative furnaces use a lattice of 

brickwork to recover waste heat from exhaust gases. Electric furnaces melt glass by passing an 

electric current through the melt. Electric furnaces are either cold-top or steel shell. Cold top 

furnaces operate during normal production using only electricity, but during startup use natural 

gas to heat the empty furnace before it is filled with cullet. These furnaces use internal cullet at 

startup because it melts readily and a molten batch can be established readily in the furnace. 

Cold-top furnaces then establish a damp crust of raw materials, and convert to all electricity 

during the remainder of the furnace life. Cold-top furnaces are open above the level of the raw 

material; they do not have furnace walls or a crown. Steel shell furnaces are similar, but they 

have steel walls and top surrounding the melt. 

Wool fiberglass is generally produced for insulation and is formed into continuous mats that are 

cut into sections called “batts”. Some facilities also produce loose wool and other specialty 

products. During the formation of fibers into a wool fiberglass mat (the process known as 

"forming" in the industry), glass fibers are made from molten glass and if the product is 

“bonded”, a chemical binder is simultaneously sprayed on the fibers as they are created. 

Historically, the binder was a thermosetting resin that holds the glass fibers together. Although 

the binder composition varies with product type, typically the binder consists of a solution of 

phenol-formaldehyde resin, water, urea, lignin, silane, and ammonia. However, most facilities 

 

1

 AP 42 Compilation of Air Pollutant Emission Factors. Office of Air Quality Planning and Standards. Fifth Edition. 

Vol. I. Chapter 11.13: Glass Fiber Manufacturing. http://www.epa.gov/ttnchie1/ap42/ch11/final/c11s13.pdf.
3 

have begun to use phenol-formaldehyde free resins, some of which do not require heat for curing 

in a thermosetting process. Of the 30 wool fiberglass facilities currently operating in the US, 20 

have completely phased out phenol/formaldehyde binders on RS lines. 

Two methods of creating fibers are used by the industry; rotary spin (RS) and flame attenuation. 

(FA). In the RS process, centrifugal force causes molten glass to flow through small holes in the 

wall of a rapidly rotating cylinder to create fibers that are broken into flexible strands in an air 

stream. In the FA process, molten glass flows by gravity from the furnace through numerous 

small orifices to create threads that are then attenuated (stretched to the point of breaking) by 

high-velocity hot air and/or a flame. After the glass fibers are created (by either process) and 

sprayed with the binder solution (if bonded), they are collected by gravity on a conveyor belt in 

the form of a mat. If a thermoset bonded product is being produced, the conveyor carries the 

newly formed wool fiberglass through a large oven to cure the thermosetting binder and then 

through a cooling section where ambient air is drawn down through the mat. The wool fiberglass 

is then cooled before trimming. This curing process is not performed if the product is not bonded 

or if the resin is not one requiring the thermosetting process. A summary of emission units as 

regulated under the subpart NNN for wool fiberglass facilities is included in Table 1. 

Table 1. Summary of Wool Fiberglass Production Emission Units

Emission Unit Regulated Process Description HAP Emitted 

Glass-Melting 

Furnace 

Furnace where raw material is melted. Metals, HF, HCl

RS Lines RS lines that produce bonded building insulation 

products (includes forming, curing, and collection 

processes). 

Formaldehyde, 

methanol, and phenol 

(from bonded products 

that use phenol/ 

formaldehyde binder) 

FA Lines FA lines that produce bonded pipe insulation and 

heavy density products (includes forming, curing, 

and collection processes). 

The current Wool Fiberglass NESHAP was promulgated on June 14, 1999 and applies to new 

and existing glass-melting furnaces, each new and existing FA manufacturing line producing a 

bonded pipe product or a bonded heavy density product, and each new and existing RS 

manufacturing line producing a bonded wool fiberglass building insulation product. 

3.0 Practices, Processes, and Control Technologies for Wool Fiberglass Production 

To determine developments in practices, processes, and control technologies, we examined the 

control technologies considered during NESHAP development and control technologies and 

advances identified through the data and information collection activities taken to support the 

Residual Risk and Technology (RTR) amendments, direct correspondence with the industry, and 

through searches of the EPA’s RACT/BACT/LAER Clearinghouse and the Internet. 

3.1 Control Technologies Considered for the 1999 NESHAP 

For the purpose of this exercise, a “development” was considered to be: 
4 

• Any add-on control technology or other equipment (e.g., floating roofs for storage 

tanks) that was not identified and considered during MACT development, 

• Any improvements in add-on control technology or other equipment (that was 

identified and considered during MACT development) that could result in 

significant additional emission reduction, 

• Any work practice or operational procedure that was not identified and considered 

during MACT development, 

• Any pollution prevention alternative that could be broadly applied that was not 

identified and considered during MACT development, and 

• Any process change that could be broadly applied that was not identified and 

considered during MACT development. 

Table 2 summarizes the practices, processes, and control technologies considered during the 

development of the 1999 MACT standard. 

Table 2. Summary of Practices, Processes, and Control Technologies Identified and 

Considered During Wool Fiberglass Production 1999 MACT Development2

Emission Source Practices, Processes, and Control Technologies 

Furnaces Fabric filter, dry and wet ESP, batch wetting 

3.2 Technology Developments After Promulgation of the 1999 NESHAP3,4

Since development of the NESHAP in the 1990’s, the methods for controlling emissions from 

furnaces are the same, but some technologies have developed that can affect the emissions of 

wool fiberglass production. We evaluated our technology review on all furnaces in the source 

category, which included furnaces at both area and major sources. At the time the MACT 

standard was promulgated in 1999, all wool fiberglass facilities were major sources. However, 

due to the phase out of phenol/formaldehyde binder, most facilities in the source category have 

changed status from major to area source. However, this change in status did not affect the 

furnace (i.e., furnaces at major and area sources are of the same design and size). Therefore, we 

believe it is appropriate to consider all furnaces in the technology review for this process. 

3.2.1 PM Emissions 

For our technology review under CAA section 112(d)(6), the EPA reviewed furnace emissions 

data provided by facilities and found that current PM emission rates achieved by the majority of 

glass-melting furnaces are significantly lower than the 1999 MACT limit. We identified 

advances in control measures for PM emissions (as a surrogate for metal HAP) including 

improvements in control technology (e.g., increased capture efficiency) and application of 

 

2

 Wool Fiberglass Insulation Manufacturing. Background Information for Proposed Standards. December 1983. 

3

 Meeting Notes. Conversation between Carlos Davis, CertainTeed, Kansas City, KS and Susan Fairchild, 

Environmental Scientist, US Environmental Protection Agency. April 14, 2011. 

4

 Meeting and Site Visit Notes. Conversation between Carlos Davis, CertainTeed, Kansas City, KS and Hugh 

McCullough, Environmental Scientist, Region 7, US Environmental Protection Agency. 2011. 
5 

electrostatic precipitators that had been made since promulgation of the 1999 NESHAP. We also 

found that PM emissions from electric furnaces are also low due to the use of baghouses, designs 

other than cold-top electric furnaces, and batch wetting of the crust above the molten glass in 

cold-top furnaces. These electric furnace designs are not new and were also used at many wool 

fiberglass manufacturing facilities at development of the 1999 MACT standard. The EPA 

grouped PM emission rate data by control device (see Figure 1) and found that the control 

technology that achieves the best PM reduction when properly operated and maintained is a 

fabric filter (or baghouse). 

In the air gas furnace, ambient air is drawn into the furnace through ports located directly above 

the natural gas ports. Because only the oxygen portion of air is used in the combustion process, 

the remainder of the volume of air is available for chemical and physical interactions in the 

furnace environment. Dry raw minerals, which are fed into the inlet of the furnace, are heated 

and melted by the natural gas and oxygen portion of the air. The air gas furnace reaches just over 

3500° F. Particulate resulting from portions of the raw minerals with higher melting points 

become entrained in the gases that exit the furnace, and the particulate is emitted along with the 

remaining volume of gases. 

When oxyfuel furnaces are used in place of the air gas furnaces, the melting temperature over 

5000°F is reached. Because in the oxyfuel furnace, only oxygen is used with natural gas, the gas 

volume is reduced as compared to a similar air-gas furnace by about 80%. The oxygen is 

consumed in the combustion process. When the melting temperature of the raw minerals is 

reached, the gases trapped within the crystalline structure of the minerals are liberated. The 

furnace gases that are emitted from the oxyfuel furnace originate mostly from the raw minerals. 

When cullet is used in place of raw minerals, the gases exiting the oxyfuel furnace are near zero. 

The lower the furnace gas volume and raw mineral content of the furnace, the lower the PM 

emissions in the furnace exhaust. The PM emissions are indirectly proportional to the raw 

mineral content of the furnace and the volume of air entering the furnace.5 

Electric furnaces both use electrodes embedded within the melt to produce molten glass during 

normal operation, and have low PM emissions as a result of the furnace design and raw material 

wetting. 

 

5

 For the same reasons, total emissions of NOx are lower in the oxyfuel furnace than in the air gas furnace. The 

concentration of CO2 in the exhaust gases of the oxyfuel furnace are higher than in the air gas furnace due to the 

lower total gas volume of the oxyfuel furnace. 
6 

Figure 1. Furnace PM Emission Rate by Control Device 

3.2.2 Chromium Compound Emissions 

Subsequent to the November 2011 notice, we issued a CAA section 114 ICR to collect emissions 

data and other information on glass-melting furnaces in order to regulate area sources in a future 

action. This ICR resulted in a near complete dataset for emissions test data on all wool fiberglass 

furnaces, with the only exceptions being furnaces at facilities that were closed or that were shut 

down at the time of the 2012 testing. Additionally, in an effort to evaluate the various types of 

furnaces used in the production of wool fiberglass, the EPA project team visited several wool 

fiberglass facilities in 2012, and industry representatives provided detailed information on each 

type of furnace. After analyzing all of the data received, the EPA identified refractories having a 

high content of chromium, and their use in wool fiberglass furnaces, as a new development 

affecting the emissions of chromium compounds from sources subject to the standard. We 

reviewed the use of chromium refractories (as compared to non-chromium refractories), the use 

of caustic scrubbers to reduce chromium in the furnace exhaust, and the current industry 

practices used to reduce chromium emissions from the furnace emissions. We analyzed the 

technical feasibility and the estimated impacts (e.g., costs, emissions reductions, risk reductions) 

of applying these developments. 

In our technology review under CAA section 112(d)(6) for chromium, we found that, while the 

furnaces and control technologies are generally the same as those used at promulgation of the 

MACT standard in 1999, there have been some developments in furnace design and preference 

in control equipment. Air-gas furnaces, once widely used throughout this industry, have been 

mostly phased out due to high nitrogen oxide (NOx) and PM emissions. In place of the air-gas 

furnace, oxyfuel furnaces are being constructed because they are more energy efficient, and 

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

PM (lb/ton)

PM (lb/ton glass pulled) 

Emission Rates By Control Device Type

 PM

Baghouses and Fabric 

Filters

Batch

Wetting

Baghouse

+ Secondary 

Control

ESP

Furnace
7 

because they emit NOx and PM at very low levels. Review of the industry literature6,7,8,9,10 and 

public comments indicate that once a source of industrial oxygen is sited in the vicinity of a wool 

fiberglass manufacturer, that facility is likely to convert from air-gas or electric to oxyfuel 

technology. 

We also found that while chromium refractories were used prior to 1999, the manufacturers of 

these products had not overcome some significant problems (such as spalling from thermal shock 

in certain high temperature applications). As a result, their use was confined to limited areas of 

the furnace that experience low thermal shock or areas in which furnace repairs and refractory 

replacement could be performed readily. 

Developments in refractory technology and in furnace design are inextricably linked. Oxyfuel 

furnaces were not widely used prior to 1999 in the wool fiberglass industry, due to a number of 

factors, especially refractory degradation in the wool fiberglass furnace environment. The then 

new technology of the oxyfuel furnace constructed using conventional refractories available at 

the time (e.g., alumina-silicate, zirconium) limited the furnace life to 4 or 5 years. As a result, 

air-gas and electric furnaces predominated in the industry prior to 1999. 

With the advent of new refractory technology, new oxyfuel furnaces were constructed since the 

1999 NESHAP that could be expected to have a longer service life. With the industry focus upon 

new furnace designs and technology, the research to develop refractories that could withstand 

high temperatures, thermal shock and corrosive materials yielded the development of new types 

of chromium refractory products (such as fused-cast chromium refractories and cast-in-place 

chromium refractories) that are used for construction of the high-temperature oxyfuel furnace. 

As a result, the wool fiberglass industry began a trend toward oxyfuel furnaces constructed using 

high-chromium refractory products, a trend that is expected to continue into the future. The 

increased use of high-chromium refractory led to the increased chromium emissions as a result of 

both wool fiberglass raw material formulation (corrosivity) and associated refractory degradation 

(i.e., furnace wear). 

Oxy-fuel furnaces have replaced all but three air gas furnaces and are expected to replace the 

remaining air gas furnaces over the next 10 years due to overall economic and production 

advantages. Oxy-fuel furnaces are fired using industrial-grade oxygen and natural gas to heat the 

furnace. They operate with higher temperatures above the melted glass (inside the furnace) than 

air gas furnaces due to the high temperature of oxygen combustion. This also results in low PM 

and NOx emissions because there are no excess gases in the furnace (as is the case for air-gas 

furnaces). 

 

6

 U.S. DOE Energy Efficiency and Renewable Energy, Industrial Technologies Program, Final Technical Report. 

“Compressive Creep and Thermophysical Performance of Refractory Materials”. Oak Ridge National Laboratories. 

June 2006. 

7

 Oxygen-Enhanced Combustion, Chapter 7. Baukal, Charles E., Jr. 1998. 

8

 “Advances in Oxyfuel Fired Glass-Melting Technology”. Hisashi Kobayashi. January 2004. 

9

 “When does oxy-fuel make sense?” Russell Hewertson, Manager of Combustion Technology, Air Products and 

Chemicals, Inc., 2005. 

10 Diagnostics And Modeling Of High-Temperature Corrosion Of Superstructure Refractories In Oxyfuel Glass 

Furnaces: Extended Superstructure Refractory Life Will Enhance Oxyfuel Firing Process. Elliott Levine, Office of 

Industrial Technologies Energy Efficiency and Renewable Energy, U.S. Department of Energy, December 2000. 
8 

Studies indicate that, under normal industrial temperatures and oxidizing conditions, trivalent 

chromium, which is present in the refractory, can oxidize to hexavalent chromium.11 It was 

found that uncombined and available oxides were responsible for a higher yield of hexavalent 

chromium. Consequently, an increasing concentration of oxides in the oxy-fuel glass-melting 

furnace environment increases the formation of chromium from the trivalent state to hexavalent 

state. The condition of high oxides in the oxy-fuel glass-melting furnace environment is one 

characteristic of the highest emitting glass-melting furnace.12 

Moreover, while the degradation of the glass-melting furnace refractory indicates increasing 

chromium emissions, that process does not necessarily follow a normal and predictable pattern. 

The degradation of refractories within the glass-melting furnace is a function of numerous 

factors, including temperature, time, stress, and the composite effects of aging and creep 

response. These processes are highly nonlinear, so the traditional equations that assume steadystate deformation rates are not appropriate.13

 

We have also found that as the refractories of the gas-fired glass-melting furnaces degrade, the 

chromium of those refractories at and above the metal/glass line is emitted as particulate to the 

outside air. Chromium from the refractories below the metal/glass line is absorbed into the 

molten glass and becomes vitrified with the other raw minerals. Industry commented that 

refractory loss from degradation of the refractory walls in use is approximately 20,000 pounds of 

refractory annually.14 However, much of the loss occurs below the glass melt line. The 

chromium released below the glass melt line is believed to stay in the glass. 

We determined that chromium emissions tend to increase with furnace age based on emissions 

test data for a facility with the highest-emitting glass-melting furnace (an oxy-fuel furnace) 

collected over a 7-year period for state inventory reporting. Table 3 shows the annual chromium 

compound emissions estimates calculated using the test results and permitted production rates. 

The table shows that in 2004, chromium emissions were estimated to be less than five pounds 

annually. By 2010, the estimated emissions for the furnace increased to 540 pounds per year. The 

emissions testing conducted in 2010 also showed that that 93 percent of the total chromium was 

in the hexavalent state. 

 

11 Lee, Y., Nassaralla, CL., Minimization of Hexavalent Chromium in Magnesite-chrome Refractory. Metallurgical

and Materials Transactions, 1998. 

12 EPA Region 7 Notes on CertainTeed Kansas City Plant. June 30, 2011. EPA-HQ-OAR-2010-1042-0067.

13 Compressive Creep and Thermophysical Performance of Refractory Materials. U.S. Department of Energy and 

Oak Ridge National Laboratory. June 2006 pp. 63.

14 Minutes of EPA Meeting with Representatives of the Wool Fiberglass Industry and NAIMA. August 31, 2011. 
9 

Table 3. Summary of Chromium Emissions from 2004 – 2010 

Year Chromium Emissions (pounds per year) 

2004 <5 

2005 30 

2008 114 

2010 540 

This glass-melting furnace was not reconstructed during this 7-year period covered by the 

chromium testing which indicates that a degradation of the chromium refractory resulted in a 

significant increase in chromium emissions during this period. We believe that this high-emitting 

glass-melting furnace clearly demonstrates a potential for increased chromium emissions for 

glass-melting furnaces where the chromium containing refractory is exposed to high 

temperatures. While this glass-melting furnace is located at a major source, we note, as discussed 

in Section 3.2, there is no difference in design and operation of a glass-melting furnaces at major 

and area sources. 

Electric furnaces do not emit chromium at the levels of gas-fired furnaces. Test data collected on 

wool fiberglass furnaces in 2010 and 2012 show that the average chromium emissions from 

electric furnaces are approximately two orders of magnitude lower than the average chromium 

emissions from gas-fired furnaces. The electric furnaces having the highest chromium emission 

rate emitted at levels similar to the gas-fired furnaces emitting chromium at the lowest measured 

rates. Electric furnaces produce glass at lower production rates (averaging is about 50 tons per 

day), as compared to gas-fired furnaces (averaging about 250 tons per day). 

Gas-fired furnaces have higher chromium emission potential for compared to electric glassmelting furnaces, due to differences in design and operation of gas-fired glass-melting furnaces. 

A chromium refractory product has the greatest resistance to heat and wear of any refractory in 

use today. The temperatures above the melt in gas-fired glass-melting furnaces range from 2500◦

to 4500◦F, while the temperatures in electric glass-melting furnaces are a few hundred degrees. 

Electric furnaces are constructed using chromium refractory at and below the glass/metal line, 

and a much smaller total surface area of chromium refractory is available for degradation and 

ensuing emission to the furnace stack as a result. Due to their higher operating temperatures, gasfired glass-melting furnaces are constructed using chromium refractories at various parts of the 

glass-melting furnace that are above the molten glass, including the crown. The presence of 

chromium above the glass melt line, high temperatures, and corrosive environment are factors 

influencing an increased chromium emission potential emissions from gas-fired furnaces. In 

addition, the high temperatures result in more of the chromium being converted to its hexavalent 

state compared to electric furnaces. 

In summary, because of the advantages of oxy-fuel glass-melting furnaces over other wool 

fiberglass glass-melting furnace technology described in the preceding discussions, we expect 

oxy-fuel glass-melting furnaces constructed of chromium refractories to replace many existing 
10 

wool fiberglass glass-melting furnaces of other designs, particularly as sources of industrial 

oxygen are sited near wool fiberglass facilities.15,16 

3.3 Correspondence with Industry

To identify new emission control technologies in use, a voluntary information request was sent 

to all U.S. wool fiberglass manufacturing facilities. To identify new technologies, facilities were 

asked to identify any controls that did not fall under the following categories: electrostatic 

precipitator (ESP), scrubber, mechanical collector, fabric filter, thermal incinerator, high velocity 

air filter (HVAF), mist eliminator, or ventilation system. Facilities did not list any control 

devices that were not previously identified. At least one wool fiberglass facility was identified as 

having a scrubber and dry ESP combination for controls on a furnace. Information from similar 

source categories showed that a sodium hydroxide (NaOH) scrubber could be used on hightemperature gas-fired furnaces to reduce acid gas emissions as well as chromium compounds 

emissions. 

Additionally, as noted in Section 3.2.2, the EPA sent out a CAA section 114 ICR in 2011 that 

required PM, chromium, and hexavalent chromium testing of furnaces to help determine the 

current levels of control at which existing technologies are currently operating. The ICR also 

required facilities to provide detailed information on the chromium contents of furnace 

refractories and their use of binders. The EPA has participated in several meetings with industry 

representatives and the wool fiberglass trade association (the North American Insulation 

Manufacturers Association, NAIMA) regarding current practices and technologies used at wool 

fiberglass plants. 

3.4 Search for Other Applicable Technology Developments 

In addition to the information discussed above, searches of the RACT/BACT/LAER 

Clearinghouse and the Internet were conducted to identify other technologies or developments 

that could be applied to wool fiberglass production. The results of these searches are described 

in the following paragraphs. 

3.4.1 RACT/BACT/LAER Clearinghouse17

 

Under EPA’s New Source Review (NSR) program, if a company is planning to build a new plant 

or modify an existing plant such that air pollution emissions will increase by a large amount, the 

company must obtain an NSR permit. The NSR permit is a construction permit which requires 

the company to minimize air pollution emissions by changing the process to prevent air pollution 

and/or installing air pollution control equipment. 

 

15 Letter from A. Crane, NAIMA to S. Fairchild, US EPA, dated January 28, 2013. 

16 Baukal, Charles, et al, Oxygen-Enhanced Combustion. Boca Raton: CRC Press, 1998. 

17 Technology Transfer Network, Clean Air Technology Center - RACT/BACT/LAER Clearinghouse. 

http://cfpub.epa.gov/rblc/index.cfm?action=Search.BasicSearch&lang=eg 
11 

The terms “RACT,”“BACT,” and “LAER” are acronyms for different program requirements 

under the NSR program. RACT, or Reasonably Available Control Technology, is required on 

sources in areas that are not meeting national ambient air quality standards (i.e., non-attainment 

areas). BACT, or Best Available Control Technology, is required on major new or modified 

sources in attainment areas. LAER, or Lowest Achievable Emission Rate, is required on major 

new or modified sources in non-attainment areas. 

BACT and LAER (and sometimes RACT) are determined on a case-by-case basis, usually by 

State or local permitting agencies. The EPA established the RACT/BACT/LAER Clearinghouse, 

or RBLC, to provide a central database of air pollution technology information (including past 

BACT and LAER decisions contained in NSR permits) to promote the sharing of information 

among permitting agencies and to aid in future case-by-case determinations. However, data in 

the RBLC are not limited to sources subject to RACT, BACT, and LAER requirements. 

Noteworthy prevention and control technology decisions and information are included even if 

they are not related to past RACT, BACT or LAER decisions. 

The RBLC contains over 5,000 air pollution control permit determinations that can help identify 

appropriate technologies to mitigate most air pollutant emission streams. It was designed to help 

permit applicants and reviewers make pollution prevention and control technology decisions for 

stationary air pollution sources, and includes data submitted by several U.S. territories and all 50 

States on over 200 different air pollutants and 1,000 industrial processes. 

To identify technologies appropriate for wool fiberglass production, searches of the RBLC were 

made using the Process Type Code: 99.033–Wool Fiberglass. All records from 1999 to 2011 

were searched. In all cases, the control devices and methods identified through the RBLC search 

do not represent new technologies for controlling HAP emissions. 

3.4.2 Internet Search 

A general search of the Internet was conducted for information on control technologies for wool 

fiberglass furnaces, and RS and FA manufacturing lines. The Internet search did not identify any 

new practices, processes, or technologies that have not already been considered in this review. 

4.0 Technology Review Findings 

4.1 Bonded Lines 

For our technology review for the bonded lines under CAA section 112(d)(6) for the Wool 

Fiberglass Manufacturing source category in the 2011 proposal (76 FR 72803), we conclude that 

emissions of formaldehyde, methanol and phenol have been significantly reduced since 

promulgation of the 1999 NESHAP due to the phasing out of phenol-formaldehyde binders. We 

did not receive any information or data during the public comment period for the 2011 proposal 

or for the 2013 or 2014 supplemental proposals that warranted revising our technology review 

for bonded lines. As discussed in section V.H of preamble to the final rule, we have issued a 

CAA section 114 ICR to wool fiberglass facilities to obtain updated formaldehyde, methanol, 

and phenol emissions and process data for RS manufacturing lines we will conduct the 
12 

technology review and evaluate RTR limits for these sources, based on the CAA section 114 ICR 

data, at a future date. 

4.2 Glass-Melting Furnaces 

4.2.1 PM Emissions 

Based on our technology review conducted under CAA section 112(d)(6), we conclude that that 

have been improvements in existing control technologies and advances in developments in 

control technologies and furnace design and operation that have achieved PM emissions levels 

that are below the level established by the 1999 NESHAP. In order to reflect current achievable 

levels (as shown in Figure 1) , the EPA is reducing the MACT floor limit for PM. In the 

November 2011 proposal, a PM limit was set under technology review, but the PM limit was 

erroneously calculated using an upper predictive limit (UPL) MACT floor methodology which 

was not appropriate. In order to determine a PM limit that reflects current practices, the EPA 

gathered all PM emission rates from furnace emission testing at major sources and calculated the 

emission rate that could be met by 99 percent of the sources for which the EPA had data. PM 

emissions rate data was available for 44 furnaces at major and area sources and the 99th

percentile of the 44 furnaces was 0.33 pounds of PM per ton of glass pulled. Therefore, the EPA 

is finalizing a PM limit of 0.33 lb PM/ton for existing and new glass-melting furnaces in order to 

reflect current achievable PM emission levels. 

4.2.2 Chromium Emissions 

Our technology review for chromium emissions from furnaces found that the use of highchromium refractories to construct entire gas-fired glass-melting furnaces for wool fiberglass 

manufacturing is a new development that began after promulgation of the 1999 NESHAP and 

that the increased use of high-chromium refractories has led to an increase in emissions of 

chromium compounds since the 1999 NESHAP was established. 

Figure 2 shows chromium emissions from gas-fired furnaces. These data, collected in 2010 and 

2012, show that most gas-fired furnaces emit chromium compounds below 1 x 10-4 lb/ton. Three 

furnaces which were tested in 2010 were repaired or rebuilt, and retested for the 2012 test 

request. In each case, chromium emissions decreased as a result of the rebuild / repair. 

Chromium emissions testing indicates that the highest well-performing furnace emits at 

2.0 x 10-4 lb/ton and that well-performing furnaces emit below 2.5 x 10-4 lb/ton, Furnaces that 

measured higher than this level have already been rebuilt, but not retested. 

Figure 2. Furnace Chromium Emission Rates by Furnace Type
13